Background A trio exome sequencing study identified a previously unreported NLRP1 gene variant resulting in a p.Leu813Pro substitution of the LRR (leucine-rich repeats) domain of the NLRP1 protein (NACHT, LRR and PYD domains-containing protein 1). This homozygous mutation was shared by two sisters with different clinical presentation: the younger sister had generalized inflammatory nodules with keratotic plugs, clinically resembling multiple keratoacanthomas, while the older had manifestations of familial keratosis lichenoides chronica. Objectives To analyse the consequences of this NLRP1 variant in two siblings with a different clinical spectrum of severity. Methods To demonstrate the pathogenicity, p.Leu813Pro was recombinantly expressed, and its effect on inflammasome assembly was assessed. Exome sequencing and RNA-Seq were performed to identify factors with potentially modifying effects on the severity of the skin manifestation between each sibling. Results The variant p.Leu813Pro triggered activation of the NLRP1 inflammasome leading to ASC (apoptosis-associated speck-like protein containing a CARD) speck formation and interleukin (IL)-1β release. The more severely affected sister had several additional genomic variants associated with atopy and psoriasis that were not present in her sibling. IL-5 and IL-17 emerged as dominant cytokines driving prominent inflammation in the skin of the severely affected sibling. Conclusions To the best of our knowledge, this is the first report of a NLRP1 variant that leads to a different clinical spectrum of severity within the same sibship. IL-5 and IL-17 were the main cytokines expressed in the inflammatory lesions of the severely affected patient and might be regarded as disease modifying factors, and therefore may be considered as therapeutic targets.

Background/objectives: Lipoid proteinosis (LP) is a rare autosomal recessive multisystem disorder that is caused by loss-of-function pathogenic variants in the extracellular matrix protein-1 (ECM1) gene. The typical clinical manifestations of LP include hoarseness of voice, beaded papules on the eyelids, infiltration and scarring of the skin and mucosa, as well as neuropsychological abnormalities. Currently, more than 70 pathogenic variants have been reported, including nonsense, missense, splice site, deletion and insertion pathogenic variants, and more than half of them occurred in exons 6 and 7.Methods: Clinical evaluation and Sanger sequencing were performed on eight patients from four unrelated Arab families. Results:We identified two novel ECM1 variants, one nonsense pathogenic variant in exon 6 (c.579G>A, p.Trp193*) and a deletion of three nucleotides (c.1390_1392del, p.Glu464del) in exon 9, and two previously reported frameshift variants; c.692_693delAG, in exon 6 and c.11dupC in exon 1.Conclusions: Although all patients had characteristic manifestations of lipoid proteinosis, we observed intrafamilial phenotypic variability. Our data expand the pathogenic variant spectrum of ECM1 and also supports the fact that exon 6 is one of the most common hot spots of pathological variants in ECM1. K E Y W O R D S ECM1, extracellular matrix protein 1, lipoid proteinosis, pathogenic variant 1 | INTRODUCTION Lipoid proteinosis (LP) is a rare autosomal recessive genodermatosis (OMIM 247100), characterized by deposition of an amorphous hyaline-like material in the skin, mucosa, and internal organs. 1 Since its first description by Urbach and Wiethe in 1929 2 about 500 cases have been reported worldwide. 3Clinically, LP is characterized by a wide range of manifestations with variable severity and a slowly progressive course. 1 In most cases, the first clinical sign is a hoarse cry or voice, which develops soon after birth or during infancy, and is caused by laryngeal infiltration. 4 Subsequently, skin and mucous membrane changes develop during the first few years of life, or even later. During childhood, the skin may be easily damaged by minor trauma or friction, resulting in